Actually, there are two springs, one on either side of the garage door, and at the moment, one of them is not broken, a decrease of one from the day before. (The sound isn’t sprrroingy in the least; it’s a sharp but unresonant Bam!, the sort of noise you’d get if you ordered a robot to bitch-slap Emeril.)
Replacing both springs, I suspect, is the thing to do: I’m reasoning that the inevitable difference in tension between the new spring on side A and the old spring on side B can bring about no good, and will probably break the old spring anyway.
The Amazing Doorman! will be here presently to conduct the repairs, inasmuch as I am not about to mess around with tight coils of metal that would just love to hand off a bunch of kinetic energy, or take my hand off in the process.